Most conventional aircraft are equipped with an elevator. The elevator is a movable auxiliary airfoil attached to the tailplane (usually the horizontal stabilizer) of an aircraft, which when moved changes the distribution of lift along the cross-section of the tailplane. The stability of an aircraft is significantly determined by the displacement of the center of pressure of the resultant aerodynamic lift force. When the elevator is moved up or down, the resultant lift force produces an up or down motion in the aircraft.
As weight in the aircraft is shifted or varied, such as gas being burned, or cargo or passenger load changes, unusually heavy control stick pressures will be required to keep the aircraft in the proper horizontal attitude. To alleviate these control stick pressures and thusly pilot fatigue, an adjustable trim tab is installed on the trailing edge of the elevator and sometimes on the rudder and ailerons.
The trim tab control mechanism, located in the cockpit, allows the pilot to finely adjust the trim tab position.